there is a voice setup configurator thingy when u installed CS 1.3
Look for it, its most likely in the start menu where your CS folder resides.
Run it to configure your voice.
then u run the game, and go to controls.
One of the first things u see is a voice communication setting defaulted to the K key.
change it to whatever u like.
Then in game, u hold down the key (u see a little icon on the botton right corner of screen) talk, and people should hear u. then let go of key to stop talking.